CHAPTER VII 



BIPOLAR DIAGRAM OF THE SECOND KIND IN 

 AMPERE-TURNS 



By Prof. C. A. ADAMS, S.B., E.E. 



INTRODUCTION 



In order to make plain the transition from Fig. 27, which is 

 fundamentally 'an E.M.F. diagram, to the corresponding M.M.F. 

 Diagram, it will be necessary to develop what may be called the 

 General Vector Diagram of the Synchronous Motor. 



Referring to Fig. 72, R represents in magnitude and space phase 1 

 or direction, the resultant of the field M.M.F. F and the armature 

 M.M.F. A. The space phase of F is its direction reduced to a two- 

 pole equivalent; i.e., the direction of the axis of the field poles in 

 two-pole diagram. The space phase of A is, for a single-phase 

 machine, the average direction (with respect to field structure) of 

 the armature M.M.F., and coincides with the direction of this 

 M.M.F. when the current is a maximum, right-handed or clock- 

 wise rotation of the armature being assumed. In a polyphase 

 machine the resultant of the M.M.F.'s of the several armature 

 phases is approximately constant in magnitude and direction for all 

 parts of a revolution. The time phase of the armature current / 

 may also be represented by the direction of A; and by choosing a 

 proper scale of amperes, the vectors / and A may be made identical. 



Assuming that the reluctance of the magnetic circuit through the 

 armature and air-gap is the same in all radial directions, there will 

 result a flux, <, in the same direction as R. The rotation of the 

 armature through this flux will cause to be induced an E.M.F. 2' in 

 magnitude proportional to, and in time phase 90 behind, <i>. The 



1 A similar analysis for the alternator is given in greater detail in the Harvard 

 Engineering Journal for January, 1903. 



147 



